Electronic devices are generally integrated on dice, or chips (for example, of semiconductor material). Each die may be housed in a proper package, which protects the die at the same time allowing accessing its (die) terminals. The package comprises an insulating body that embeds the die. The insulating body exposes (package) terminals, each one connected to a corresponding terminal of the die; generally, a wire-bonding technique is used wherein conductive wires are soldered at their ends each one on the corresponding terminals of the die and of the package. The terminals of the package are used to connect it (and then the corresponding terminals of the die) to external circuits. For this purpose, the electronic device is generally mounted on a Printed Circuit Board (PCB), or simply board; particularly, in the Surface-Mount Technology (SMT) the terminals of the package are soldered on (board) tracks arranged on a main surface of the board.
The packages may have different structures. For example, Flat No-leads (FN) packages are a particular type of Surface-Mount (SM) packages wherein the terminals of the packages, for example, (terminal) pads, are exposed on a front surface of the insulating body that is mounted on the board; particularly, in Quad FN (QFN) packages the pads are arranged at all four sides of the insulating body, and in QFN-Multi Row (QFN-MR) packages multiple rows of (staggered) pads are provided at each side of the insulating body. FN packages have a small (near-die scale) footprint, thin profile and low weight; this makes the FN packages very attractive in several applications (for example, in mobile devices such as smart-phones).
The electronic devices may be subject to remarkable heating during their operation (especially in power applications); therefore, the packages are generally provided with one or more heat sinks that facilitate the dissipation of the heat. For example, in the FN packages the die is mounted on a dissipation (or die) pad that is exposed on the bottom surface of the insulating body (for transferring the heat to the board). An additional heat sink may also be mounted on a back surface of the insulating body (for transferring the heat to the air). However, the insulating body generally hinders the transfer of the heat outside the package; this may reduce the performance of the electronic devices, down to cause their failure.
Moreover, the wire-bonding technique does not allow further reducing the thickness of the electronic devices. For example, the thickness of the FN packages may hardly be reduced below 0.6 mm even in Ultra-thin QFN (UQFN) packages. In this case, it also not possible to arrange the terminal pads in a central area of the insulating body (taken by the dissipation pad), with a consequent difficulty in further reducing the footprint of the FN packages.
A manufacturing process of the electronic devices may also be relatively complex, and then expensive (with a negative effect on the overall cost of the electronic devices). For example, FN packages may be manufactured from a lead-frame formed by a metal plate with a top surface that is etched to define raised areas for the (terminal and dissipation) pads. The die is attached onto the dissipation pad and its terminals are wire-bonded to the corresponding pads; the insulating body is then molded over the structure so obtained. The insulating body may embed the die completely (to reduce the manufacturing cost). Alternatively, the insulating body may be open to define a cavity housing the die; a cap is then used to seal the cavity so as to make it air-tight (to improve the performance of the electronic device). In both cases, at this point any excess metal is back-etched from the lead-frame so as to separate the terminal and dissipation pads. However, the above-described manufacturing process requires selective etching operations that are quite difficult.